Morphological and anatomical effects of abscisic acid (ABA) and fluridone (FLU) on the growth of rice mesocotyls

It has been reported that abscisic acid (ABA) promotes the growth of rice mesocotyls. We investigated the effects of ABA and fluridone (FLU), an inhibitor of ABA biosynthesis, on the morphological and anatomical characteristics of the mesocotyl of dark-grown rice seedlings. By 5 days after sowing (DAS), the mesocotyl of control seedlings had reached their a maximum length of 50.0 mm. In ABA treated seedlings, the mesocotyl continued growing until 12 DAS, reaching a length of 152.6 mm. Mesocotyls treated with FLU elongated until 4DAS attaining a final length of only 10.5 mm. The data indicated that the greater length of mesocotyls in seedlings treated with ABA was mainly due to their longer growing period. An anatomical study showed that the cell division activity of the mesocotyl localised near the coleoptilar node and that ABA prolonged the cell division activity of the meristem. The results suggested that ABA regulates the growth of rice mesocotyls by controlling the activity of the meristem localised near the coleoptilar node.